The VASA protein was identified in Drosophila as a component of the germplasm that encodes a DEAD-family ATP-dependent RNA helicase (Liang et al. (1994), Development, 120:1201-11; Lasko et al. (1988), Nature 335:611-17). The molecular function of VASA is directed to binding target mRNAs involved in germ cell establishment, oogenesis, and translation onset (Gavis et al. (1996), Development 110:521-28). VASA is required for pole cell formation and is exclusively restricted to the germ cell lineage throughout development.
Vasa homolog genes have been isolated in various animal species, and VASA can be used as a molecular marker for the germ cell lineage in most animal species (Noce et al. (2001), Cell Structure and Function 26:131-36). Castrillon et al. (2000), Proc. Natl. Acad. Sci. (USA) 97(17):958590-9590, for example, demonstrated that the human Vasa gene is expressed in ovary and testis but is undetectable in somatic tissues.
The existence of mammalian female germline stem cells, also known as oogonial stem cells or ovarian stem cells (OSCs) or egg precursor cells, in the somatic tissue of mammalian ovaries was first described in Johnson et al. (2004), Nature 428:145-50, and has now been confirmed by other research groups (e.g., Zou et al. (2009), Nature Cell Biology, published online DOI: 10.1038/ncb1869; Telfer & Albertini (2012), Nature Medicine 18(3):353-4). The potential use of OSCs to produce oocytes for use in artificial reproduction technologies (ART), including in vitro fertilization (IVF), or as sources of highly functional mitochondria for mitochondrial transfer to oocytes, as well as the use of OSCs to treat various symptoms of menopause, have been described in the scientific and patent literature (e.g., Tilly & Telfer (2009), Mol. Hum. Repro. 15(7):393-8; Zou et al. (2009), supra; Telfer & Albertini (2012), supra; White et al. (2012), Nature Medicine 18(3):413-21; WO 2005/121321; U.S. Pat. No. 7,955,846; U.S. Pat. No. 8,652,840; WO2012/142500; U.S. Pat. No. 8,642,329 and U.S. Pat. No. 8,647,869).
When OSCs were first characterized by Johnson et al. (2004), supra, it was demonstrated that the cells expressed the VASA protein, and antibodies against the VASA protein have been used to isolate OSCs from ovarian tissue homogenates (e.g., Zou et al. (2009), supra; White et al. (2012), supra). Moreover, White et al. (2012), supra, demonstrated that antibodies to an N-terminal domain of VASA could not be used to isolate viable VASA-expressing OSCs whereas antibodies to a C-terminal domain could effectively isolate the cells, suggesting that the C-terminal domain, but not the N-terminal domain, was extracellular and thus accessible to the antibodies.
The production of anti-VASA polyclonal antibodies was first described in Castrillon et al. (2000), supra, and WO01/36445. Polyclonal antibodies directed to the C-terminal portion of human VASA protein are commercially available from Abcam plc (Cambridge, UK; Product Code AB13840), and R&D Systems, Inc. (Minneapolis, Minn.; Catalog No. AF2030), and a monoclonal antibody directed against the N-terminal portion of human VASA is also commercially available from R&D Systems, Inc. (Minneapolis, Minn.; Catalog No. AF2030),
There remains, however, a need for high affinity antibodies directed to the C-terminal extracellular domain of VASA for identifying (e.g., by immunohistochemistry or labeled antibodies) and isolating (e.g., by magnetic or fluorescence activated cell sorting) cells, including but not limited to OSCs, expressing VASA.